Hitherto, a composite reverse osmosis membrane comprising a porous support having formed thereon a thin film having a substantially selective separability is known as a reverse osmosis membrane having a different structure from an asymmetric osmosis membrane.
At present, many composite reverse osmosis membranes each having formed on a support a thin film comprising a polyamide obtained by an interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide are known as disclosed in, e.g., JP-A-55-147106 (corresponding to U.S. Pat. No. 4,277,344), JP-A-62-121603 (corresponding to U.S. Pat. No. 4,761,234) and, JP-A-63-218208 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Further, a composite reverse osmosis membrane having formed on a support a thin film comprising a polyamide obtained by an interfacial polymerization of a polyfunctional aromatic amine and a polyfunctional alicyclic acid halide is known as disclosed in, e.g., JP-A-61-42308 (corresponding to U.S. Pat. No. 5,254,261).
The composite reverse osmosis membranes described above have a high desalting performance and a high water permeability, but it has further been desired for those membranes to improve the water permeability while keeping the high desalting performance from the point of efficiency, etc. For these requirements, various kinds of additives are proposed as described in, e.g., JP-A-2-187135 (corresponding to U.S. Pat. No. 4,872,984). However, in the conventional composite reverse osmosis membranes, the improvement of the water permeability is still insufficient even where these additives are used, and a composite reverse osmosis membrane having a higher water permeability has been desired.